Debris-flow disaster is one of the major types of geological disasters in China. Currently, more concern is paid to the secondary disasters which result from the blockage of the main river due to debris flow, e.g. barrier dam and dammed lake formed by debris-flow deposit inundating the upstream areas. On Aug. 8, 2010, a large debris flow broke out at Sanyanyu, Zhouqu County, Gansu Province, which filled up and buried the county town, blocked the main river—Bailong River to form a dammed lake, inundated nearly half of the county town and caused serious casualties and property loss. On Aug. 13, 2010, a large debris flow broke out at Wenjiagou Village, Qingping Township, Mianzhu City, Sichuan Province, which blocked the main river, caused more than ten death and missing filled up and buried a lot of reconstructed civilian buildings after the Wenchuan Earthquake.
With the economic development of mountainous areas and the deepening of Western Development of state policy, the demand for the debris-flow control project becomes stronger and stronger. The influence of main river transport capacity was rarely considered in the past debris flow prevention design. Due to the imbalanced distribution of amount of debris borne by each countermeasure structure, even though the debris-flow prevention works like drainage canal, sediment storage dam and deposit stopping field were built, the situation of main river blocked by debris flow still appeared and even this situation was aggravated due to excess drainage.
To prevent the occurrence of secondary disasters caused by the blockage of the main river due to debris flow, the main river transport capacity must be fully considered in the debris-flow prevention design. The debris-flow substance must be rationally distributed along the way and the debris-flow body which is drained beyond the main river transport capacity must be avoided to enter into the main river and thus cause flood inundation or outburst disasters, so as to safeguard the safety of towns, major projects and infrastructure at the mouth of debris flow gully.